Effect of Tb3+ Concentration on the Optical and Vibrational Properties of YBO3 Tri-doped with Eu3+, Ce3+, and Tb3+
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Structural and optical studies are reported of yttrium orthoborate YBO3 when tri-doped with Eu3+, Ce3+, and Tb3+, focusing on the role of terbium concentration. Incorporation of Tb3+ affects emission properties for photoluminescence (PL) excited by near ultraviolet light. For constant cerium and europium concentrations, increasing the Tb3+ results in diminished PL from the Ce3+ and Tb3+ color centers. Simultaneously, the PL excitation bands related to both Ce3+ and Tb3+ increase in intensity for red emission from the Eu3+. Results are consistent with a Ce3+ → (Tb3+)n → Eu3+ energy transfer scheme, where (Tb3+)n denotes a chain incorporating n terbium ions. A high red to orange PL intensity ratio is obtained, ranging from 1.34 to 2.09. Raman vibrational bands show a systematic change, with Tb3+ concentration, in the B3O9 ring terminal oxygen bending mode coordinated with the yttrium site where dopant ions substitute. The structural changes are interpreted as variations in the local neighborhood of these sites in the YBO3:Ce3+,Tb3+,Eu3+ crystal structure.